Discharge tube having a metal envelope



i 17, 1935. A. BoUwERs DISCHARGE TUBE HAVING A METAL ENVELOPE Filed Aprile, 1931 um" rnv..

Patented Dec. 17, 1935 UNITED STATES i DISCHARGE TUBE HAVING A-MET-AL ENVELOBE Albert Bouwers, Eindhoven, Netherlands. lassignor to N.*V. Philips 'Grloeilalnpenfabrieken, Eindhoven, Netherlands Application April 6, 193l, Serial No. 5285199 In the Netherlands April 16,1930

14' Claims.

'Ihe inventionrelatesto dischargetubes, more particularlyX-ray tubes, in which'the discharge path is surrounded bya conducting wall insulated from the electrodes, and which tubes are surrounded either entirely or partly by a metal envelope.

Such a metal envelope aords an excellent means for the attachment or support of the discharge tube, in which event it will be desirable in most cases that this member has ground-potential.

In some cases it has proved undesirable to directly ground the conducting wall surrounding the discharge path and constituted by aK portion of the wall of the tube whichconsists entirely of metal or by ,a conducting coating of said wall. However it may beadvsable to fix theH potential Vof the wall portion.

.maygbe constituted by an, auxiliary discharge-gap. .In order. to-.ensure vthat. thepotential of the wall has. as constantia Ivalue as possible,. :use may be made oi aresistance the'conductivitypfwhich increases with thev current intensity. Alternatively, use may .be .made oi .-a;resis tance Winch only becomes conductive above. a determined: voltage but which below this voltage passes substantially .no'current 'It may also be advantageous;to .usebetween the wall and the envelope afconnectionwhose conductivity increasesrwith the temperature.

The connecting -resistance .may be Jentirely enclosed between the `wall of 1 the .envelope and in this case it Vmay--be constituted, -fornexample,`by a conducting orsemi-conducting intermediate layer. It-may-also be constituted by a wire or band which iswound coaxially with the tube and which may be enclosed entirely or partly in an intermediate layer ofv insulating-material. In the latter case a very useful construction is obtained by giving the resistancev the shape of a spiral drawn out in the direction of the axis of the tube.

The invention-is of particular importance with .X-ray tubes but it may.also be applied to other tubes, for-example to valve-tubes, usually termed rectii'iers.

The invention will be more,A clearly understood by referring to the accompanying drawing which -capacity and which connect the wall I to the elec- 15 trodes of the tube, towit to the anode 4 and the cathode5. `The latteris a filament 4vsurrounded by aime tallic focussing device. The wall I is surrounde d- ,in itsturn by a metal envelope 1.

If theincandescible cathode is arranged in such 20 manner thatthe Wall I is struck by electrons, this wall mayacquire a. charge which counteracts a uniform distribution Yo1 the potential. For the dissipation of this charge there'has been provided between the. walll and the` envelope 'I an 25 intermediate layer 8 consisting of a material which has a high resistance but suiiicient conductivity to dissipate .undesirable charges.

In Fg. 2which represents a portion of the wall of the tube, and in which the electrodes have 30 4been omitted, I I denotesa metal Wall correspondingto the .wall I of Figure 1. To the wall II are 4secure i, .w ith the interposition of insulating cylinders vI4 and' I5, metal envelopes IZand I3 which may r-be connected to ground. Between envelopes 35 I2eand I3 and the wall I I is connecteda resistance I6, constituted ,hva spark gap. Instead of a spark gap, use may also be made of an ordinary Aohmic resistance or again lofa particular resistance having, for example, a conductivity which in- 40 creases vwith an increasing current intensity. AUse may be made 4inter alia cian enclosed discharge, such as a glow, discharge. Neither is it necessary for, the resistance to be located in the space between thewall and the envelope. 45 Figure ShQws armoede of construction in which the resistanceis constituted bya Spirally Wound wirei 2l which hasbeendrawn out in the direction of the axis of the tube and which connects the wall 22 to the enve1ope23, the wirek 2I being enclosed in an insulating massy 24 which absorbs X-rays. In this form of construction a resistance, for a rather large power can vbe housed in a'lmited space. -ABesides, a correct-distribution ofthe `electric load of the insulating material 24 55 is facilitated thereby. As stated above, the re- -sistance 8 or 2| may advantageously be of material having a negative temperature coefficient of resistance so that it conducts current more readily as its temperature increases.

What I claim is:

1. In an electric discharge tube, electrode members between which during the operation of the tube a high potential diierence occurs, said members being spaced apart to provide a discharge gap, a metal section insulated from the electrode members and surrounding the discharge gap and the operative portions of the electrode members, a metal sleeve surrounding said metal section and insulated from said electrode members, and a substantial electric resistance for limiting the flow of electric current between said metal section and the surrounding metal sleeve.

2. In anV electric discharge tube, a metal section surrounding a portion of the discharge space of the tube and subjected to the impingement of free electrons, a metal sleeve surrounding the tube and insulated from the operative elements thereof, and an electric resistance for limiting the flow of electric current between said metal section and said sleeve.

3. In an X-ray tube having electrodes spaced from each other so as to form a discharge gap, an enclosing envelope mechanically connecting the electrodes and embodying at least one part of conductive material causing a section of said wall to possess the same potential throughout its entire area and extending over the discharge gap, means for supporting the tube comprising a metal sleeve surrounding the tube and said part of conductive material but electrically separated from the latter and adapted to be grounded during the operation of the tube, said sleeve being insulated from the electrodes of the tube for substantially equal voltages, and a substantial electric resistance forming a connection between the sleeve and the part of conductive material.

4. An enclosing envelope having a conductive area, an electric discharge tube mounted therein comprising a closed wall, an anode member and a cathode member mounted in said wall, said members being electrically insulated from said conductive area for substantially equal voltages, said wall comprising a metal section surrounding the operative portions of said members and insulated from the electrodes for substantially equal voltages, said metal section being located within said enclosing envelope in spaced relation with said conductive area, and an electric resistance arranged in the space between the enclosing envelope and the metal section, said resistance connecting the said metal section with said conductive area.

5. A metal envelope, an electric discharge tube mounted therein, said tube having electrode members and an equipotential waist section insulated from the electrode members, said metal envelope having a central portion supporting the said waist section of the tube, and a layer comprising an electric resistance interposed between said envelope and waist section, said resistance conducting during the operation of the tube avsufiicient quantity of electricity to establish a potential difference between said waist section and said envelope.

6. In combination, a hollow metal supporting member, an electric discharge tube mounted therein, said tube having electrode members and a central equipotential Waist section, insulating supporting means interposed between the discharge tube and the supporting member, said waist section being situated within the hollow supporting member, and an electric resistance connecting said waist section and said supporting member, said resistance having a conductivity which increases with the intensity of an electric current iowing through it.

7. In combination, a hollow metal supporting member, an electric discharge tube mounted therein, said tube having electrode members and 10 a central equipotential waist section, insulating supporting means interposed between the discharge tube and the supporting member, said waist section being situated within the hollow supporting member, and an electric resistance connecting said waist section and said supporting member, said resistance having a conductivity increasing proportionally with the intensity of an electric current flowing through it.

8. In combination, a hollow metal supporting member, an electric discharge tube mounted therein, said tube having electrode members and a central equipotential waist section, insulating supporting means interposed between the discharge tube and the supporting member, said waist section being situated within said hollow supporting member, and means for limiting the flow of electric current between the said Waist section and said supporting member including a conductive path which above a predetermined voltage shows a considerable decrease of resistance.

9. In combination, a' hollow metal supporting member, an electric discharge tube mounted therein, said tube having electrode members and a central equipotential waist section, insulating supporting means interposed between the discharge tube and the supporting member, said waist section being situated within said hollow supporting member, and means including an elec- 40 tric discharge gap with independent 4discharge for electrically connecting said waist section and supporting member.

10. In combination, a hollow metal supporting member, an electric discharge tube mounted therein, said tube having electrode members and a central equipotential waist section, insulating supporting means interposed between the discharge tube and the supporting member, said waist section being situated within said hollow supporting member, and a conductor for permitrting the passage of a limited electric current between the said waist section and said supporting member, the resistance of said conductor decreasing with the temperature.

11. A device comprising an electric discharge tube provided with a conductive waist portion and insulating wall portions of substantially equal insulating capacities at both sides thereof, each carrying an electrode member, a conductive envelope surrounding said tube and leaving a space around the said waist portion of the tube, an

insulating layer in said space and a lamentary resistance enclosed by said layer which is coaxially wound with the tube, said resistance having one end in contact with said conductive waist portion and its other end with said conductive envelope.

12. A device comprising an electric discharge tube provided with a conductive Waist portion and insulating wall portions of substantially equal insulating capacities at both sides thereof,

Y* each carrying an electrode member, a conductive envelope surrounding said tube and leaving a space around the said waist portion of the tube,

an insulating layer in said space, and a ilamen-V tary resistance embedded in said layer which is coaxially wound with the tube and has the shape of a spiral drawn out in the direction of the axis of the tube, said resistance having one end in contact with said conductive waist portion and its other end with said conductive envelope.

13. An X-ray installation comprising an X-ray tube having a cathode and an anode, the Wall of said X-ray tube having an equipotential central area and insulating portions withstanding each a voltage of the same order of magnitude, said insulating portions supporting the anode and the cathode respectively in operative relation to each other and to said central area, at least one insulating member supporting said central area and being supported by a protective metal envelope which is grounded and encloses the X-ray tube,

said envelope being out of direct contact with said central area of the X-ray tube, and a substantial electric resistance permitting the passage of a limited flow of electrons from the interior of the X-ray tube over the central area of the tube Wall and the enclosing envelope to the ground.

14. A device comprising an electric discharge tube provided with a conductive waist portion and insulating wall portions of substantially equal insulating capacity at both ends thereof, each of said insulating wall portions carrying an electrode member, a conductive member surrounding said Waist portion with an intermediate space, and a layer provided in said space, said layer being of a material which permits the passage 15 

